There are widely known mercury or mercury-wetted contacts for switching devices, comprising a solid metal base made of platinum, iron, nickel, or else of metals of the chromium subgroup, viz. tungsten, molybdenum, as well as the methods of manufacture of such contacts, including wetting the cleaned and degreased solid metal base (made of iron and nickel) with mercury by periodic dipping of the base into a mercury-containing liquid medium.
The noble metals acting as the base of the hitherto known mercury contacts are prone to forming intermediate phases and chemical compounds with the mercury, which matter accumulates at the contact junction and eventually affects the electric and dynamic characteristics of the mercury contact, and, hence, its reliability and durability.
The hitherto known mercury contact having iron for its solid metal base is produced by periodically dipping the precoated iron base into a sodium amalgam through either a weak solution of a mineral acid or water.
(See, for instance, "Working With Mercury Under Laboratory And Production Conditions" by P. P. Pugatchevitch, in Russian, NAUKA Publishers, Moscow, 1972, p. 183).
Iron, as well as nickel and the metals of the chromium subgroup practically will not react with mercury. However, these metals are thermodynamically unstable on account of their being electrochemically active. This activity is significantly enhanced by a contact with mercury featuring a high positive potential.
Consequently, the contact junction is not resistant against electrochemical processes resulting in either partial or complete lack of adhesion between the solid metal and mercury. The probability and intensity of these processes are dependent on the quality of the initial wetting of the solid metal with mercury.
The hitherto known method does not provide for adequately wetting the surface of the above mentioned solid metals with mercury, on account of microcavities left in most cases at the contact junction under the mercury film and containing an electrochemically active fluid, e.g. the remains of acid, water and other electrolytes employed by the production process.
These microcavities act as the nuclei of degrading electrochemical processes affecting the stability and durability of the solid metal-mercury contact junction.
It is an object of the present invention to provide a mercury contact wherein the solid metal base is highly electrochemically stable and inert with respect to mercury.
It is also an object of the present invention to provide a method of manufacturing a mercury contact, which should provide for an adequate quality wetting of the surface of the solid metal base with mercury.
This object is attained with a mercury contact wherein, in accordance with the invention, the mercury-wetted solid metal base is made of beryllium.
The object of the invention is further attained in a method of manufacturing a mercury contact, including periodically dipping the cleaned solid metal base of the contact into a liquid medium containing mercury, in which method, in accordance with the present invention, the solid metal base of beryllium is dipped into chemically pure mercury through a mixture containing a saturated solution of chromic anhydride in water and 40 per cent solution of hydrofluoric acid in water, taken in a 1:1 ratio by volume.
The disclosed mercury contact and the method of its manufacture provide for adequate quality of wetting the surface of the solid metal base with mercury (no microcavities are present) and therefore substantially reduces the electrochemical activeness of the solid metal base in the event of engagement with mercury, whereby the stability and durability of the mercury contact are enhanced.